1. Field of the Invention
The present invention relates to a method for preparing a radioisotope-labeled compound using a carbon nanotube.
2. Description of the Related Art
Nuclear medicine, a branch of medicine pertaining to the diagnostic, therapeutic, and investigative use of radioactive chemical elements, requires radionuclides or pharmaceuticals labeled with radionuclides (radiopharmaceuticals) for the practice thereof. The operation of a nuclear reactor produces numerous kinds of radioisotopes. From among them, some radioactive species suitable for use in diagnosis or therapy are selected, and then processed into pharmaceuticals administrable to human bodies. Such radiopharmaceuticals guarantee defined images of lesions, readily giving information on, for example, the metastasis of cancer, which is difficult to detect using other methods.
Hepatic diseases occur particularly frequently in Asians, including Koreans. At present, liver function tests are becoming the most important diagnostic assays. Liver function tests include the use of radioisotopes to obtain nuclear scintigraphs which give important information about local lesions of the liver as well as the size, shape and gross function of the liver.
There occur diffuse diseases and local diseases in the liver. Diffuse diseases of the liver include acute hepatitis, chronic hepatitis, liver cirrhosis, injuries caused by drugs, such as alcohol, and connective tissue injury. Patients with diffuse diseases show low functioning of the liver, which can be easily detected by radionuclide imaging or nuclear scintigraphy. Hepatoma is representative of the local diseases of the liver. Imaging of the liver gives information about the location and size of the mass, as well as about the function of the liver.
Liver cancer may be caused by the metastasis of various malignant tumors as well as primary hepatoma. Success in cancer therapy depends on the control of metastasis. In images of the liver, metastatic cancer appears as a local defect. However, images of similar defects are caused by various benign lesions, normal hepatic structures, and artifacts. Therefore, the understanding of such factors is a prerequisite for reading images of the liver.
Radiopharmaceuticals for use in therapy employ radionuclides which are generally longer in half-life and weaker in penetration capability, but emit stronger radiation, sufficient to kill cells, in relation to that for use in diagnosis. Alpha ray-emitting radionuclides are excluded from radiopharmaceuticals for the reason that they are highly radioactive and difficult to purchase and to attach to other compounds. All of the radionuclides currently used in pharmaceuticals are species that emit beta rays.
As mentioned above, radiopharmaceuticals, whether for use in therapy or diagnosis, are prepared by labeling pharmaceuticals with specific radionuclides. Technetium-99m (99mTc) is known as the radioisotope most widely used to label radiopharmaceuticals. Technetium-99m has a half life of as short as 6 hours and emits gamma rays at 140 KeV, and thus it is not so toxic to the body. In addition, gamma radiation from the radioisotope is highly penetrative enough to obtain images. Thanks to these advantages, technetium-99m finds a broad spectrum of therapeutic and diagnostic applications in the nuclear medicine field (Sivia, S. J., John, D. L., Potential technetium small molecule radiopharmaceuticals. Chem. Rev. 99, 2205-2218, 1999; Shuang, L., Edwards, D. S., 99mTc-Labeled small peptides as diagnostic radiopharmaceuticals. Chem. Rev. 99, 2235-2268, 1999).
Methods of labeling 99mTc-2,6-diisopropylacetanilidoiminodiacetic acid are well known in the art (Callery, P. S., Faith, W. C., et al., 1976. Tissue distribution of technetium-99m and carbon-labeled N-(2,6)-dimetylphenylcarbamoylmethyl iminodiacetic acid. J. Med. Chem. 19, 962-964; Motter, M. and Kloss, G., 1981. Properties of various IDA derivatives. J. Label. Compounds Padiopharm. 18, 56-58; Cao, Y. and Suresh, M. R. 1998. A Simple And Efficient Method For Radiolabeling Of Preformed Liposomes. J Pharm Pharmaceut Sci. 1 (1), 31-37).
Basically, the conventional methods are based on the following reaction formula. In practice, a solution of SnCl2.2H2O, serving as a reducing agent of technetium-99m, in 0.1 N HCl and 0.1 ml (10 mCi) of sodium pertechnetium were added to lyophilized 2,6-diisopropylacetanilidoiminodiacetic acid in a vial, followed by stirring at room temperature for 30 min to prepare 99mTc-2,6-diisopropylacetanilidoiminodiacetic acid. The preparation of 99mTc-2,6-diisopropylacetanilidoiminodiacetic acid may be realized according to the following reaction formula.

Such conventional processes of preparing radiopharmaceuticals labeled with technetium-99m can be divided into reactions between the radioisotope and a physiologically active material to be labeled and the separation of labeled compounds from unlabeled compounds.
However, conventional labeling methods are disadvantageous in terms of the long reaction time period, the exposure of the workers to radiation, and radioactive waste. Therefore, there is a need for reaction conditions under which labeling can be more simply and rapidly conducted.
Recently, novel or improved physical properties have been found in the sub-micron world on a scale as small as nanometers. Particularly, active research is focused on carbon nanotubes (CNT), which can be used as a carrier for active materials for various organic/inorganic reactions, thereby realizing novel physical properties which find valuable applications in various industries.